This invention relates to a method and apparatus for controlling an infinitely variable transmission in which the transmission ratio is selected automatically in a first operating mode, and can be selected by the vehicle operator in a second operating mode. German Patent Document DE 41 20 540 C1, for example, discloses an infinitely variable transmission which simulates a stepped transmission, and which can be influenced directly by the driver.
In general, the transmission ratio adjustment (more precisely, the adjustment of the line pressure) in an infinitely variable transmission is designed for automatically implemented, steady and slower adjusting operations. In order to carry out these adjusting operations in a material-saving manner and without disturbing vibrations, the adjustment of the transmission ratio is provided with a high degree of damping, either in the transmission ratio control system, which carries out the determination of the transmission ratio to be adjusted, or in an adjusting device which adjusts a preset transmission ratio by changing the pressures acting upon adjusting elements of the transmission.
In simulating a stepped transmission, such as disclosed in DE 41 20 540 C1 referred to above, transmission ratio changes must be carried out within as short a time period as possible, and after a transmission ratio change, the transmission ratio is then kept essentially constant. However, this is not possible with the described high degree of damping because, as a result of the damping, fast changes of the transmission ratio are prevented.
The object of the present invention is to provide a control system for a vehicle transmission which alleviates the latter deficiency, by providing a degree of damping during adjustment of the transmission ratio, which is adapted to the selected operating mode: In the automatic operating mode, a high degree of damping is used, and therefore a high degree of comfort is achieved as well as low wear and low energy expenditures for adjusting the transmission ratio. In the manual operating mode, on the other hand, a low degree of damping is provided in order to simulate as precisely as possible the shifting represented by transmission ratio jumps.
According to one embodiment of the invention, the arrangement of the damping devices in an adjusting device is implemented in a particularly simple manner by making the adjusting device separate from the actual transmission ratio control. In addition, the adjusting device directly takes into account all hydraulic influencing variables which affect the adjustment of the transmission ratio on the transmission, so that it may be sufficient at this point if the degree of damping existing devices or functions can be controlled.
Arrangement of the damping device in a transmission ratio control system, which determines a desired transmission ratio, has the advantage that the degree of damping has a targeted effect only when the desired transmission ratio is given. It is a prerequisite that the adjusting device which follows has a degree of damping which is smaller than the smallest degree of damping used within the damping device.
In another embodiment, two damping devices, each with a fixed degree of damping, are arranged directly at the output of devices for determining the desired transmission ratio in the first and the second operating mode. This embodiment is simpler than the above-mentioned arrangements because, as a result of the direct assignment to the operating modes, a switching device for the degree of damping is not required.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.